1. Field of the Invention
This invention relates to a semiconductor package.
2. Description of the Related Art
Generally, plastic packages, metallic packages, and ceramic packages are used for packaging semiconductor chips. In regard to structure, DIP (dual inline package) and QFP (quad flat package) both using a lead frame, PGA (pin grid array) using a lead pin, and BGA (ball grid array) using solder bumps as input and output terminals are known.
In these package structures, the packages which use a lead frame enjoy simplicity of structure and allow inexpensive manufacture and, therefore, have been finding extensive utility in various kinds of semiconductor chips. Especially, the QFP is profusely used because it admits an increase in the number of input and output signals to a considerable extent and exclusively fits surfacial packaging.
Recently, the rapid advance in the technologies for the manufacture of semiconductors has come to urge increasingly high integration of semiconductor chips and compel incessant growth in the number of input and output signals per chip. As a natural consequence, the packages to be used for containing such a highly integrated semiconductor chip are expected to permit connection of semiconductor chip to multi-terminal channels at a narrow pitch.
In the conventional QFP, however, the lead frame used therein is manufactured by etching a thin sheet of such a Fe--Ni type alloy as 42 wt % Ni--Fe or 29 wt % Ni-16 wt % Co--Fe. The QFP, therefore, is at a disadvantage in limiting the lead pitch to the neighborhood of 100 .mu.m and permitting no further increase either in the size of pitch or in the number of terminals. If the number of terminals is increased at such a lead pitch as is mentioned above, the package itself will naturally grow in volume and inevitably fail to satisfy the persistent demand for miniaturization of various electronic devices. Further, since the increase under discussion adds proportionately to the total length of wirings to be distributed in the package, it will inevitably entail a delay of signal. The lead frame made of the Fe--Ni type alloy mentioned above is also deficient in electrical properties. When the signal to be handled operates at a very high speed, therefore, the voltage level of the output signal will be lowered and the noise level thereof will be heightened as an inevitable consequence.
As means to package a semiconductor chip which has a large number of input and output terminals, a method which comprises joining the semiconductor chip to a tape carrier, popularly called a tape of the TAB (tape automated bonding), and containing the TAB chip in a given package has been known in the art. The package which uses the conventional TAB chip, however, is at a disadvantage in proving structurally expensive because it necessitates connection between a connecting pad which is connected through the medium of internal wirings to input and output pins serving as external connecting terminals and lead wires which are provided in the tape carrier.
The art is not ignorant of such an inexpensive package as has a TAB chip itself sealed therein with resin. The package of this structure has a conspicuously low capacity for radiating heat and hardly admits such a highly integrated semiconductor chip as mentioned above. Further, for the package which uses the TAB chip, a structure having a metallic sheet attached fast to the TAB tape part for the purpose of preventing the so-called lead skews, i.e. bends and warps in the lead wire, has been proposed (JP-A-06-69,275). This structure, however, is at a disadvantage in attaining no improvement in the capacity for heat radiation and entailing the possibility of short-circuiting the lead wires with the metallic sheet. Further, the metallic sheet used in the package causes an erroneous operation in the package as by picking up an external noise by virtue of the so-called antenna effect. The structure also poses various problems because the metallic sheet gathers rust and sustains warps due to low rigidity.
Such conventional packages as QFP which use a lead frame as described above are at a disadvantage in imposing a limit on the lead pitch and hampering all efforts to narrow the pitch further and permit an increase in the number of terminals. The packages which use a TAB known as means to package a semiconductor chip having numerous input and output terminals are at a disadvantage in being structurally expensive, possessing an unduly low capacity for heat radiation, and suffering ready occurrence of short circuits and erroneous operations.